pre-2018 unused overall domestic loss
(5) Election to increase percentage of taxable income treated as foreign source (A) In general If any pre-2018 unused overall domestic loss is taken into account under paragraph (1) for any applicable taxable year, the taxpayer may elect to have such paragraph applied to such loss by substituting a percentage greater than 50 percent (but not greater than 100 percent) for 50 percent in subparagraph (B) thereof. (B) Pre-2018 unused overall domestic loss For purposes of this paragraph, the term “pre-2018 unused overall domestic loss” means any overall domestic loss which— (i) arises in a qualified taxable year beginning before January 1, 2018 , and (ii) has not been used under paragraph (1) for any taxable year beginning before such date. (C) Applicable taxable year For purposes of this paragraph, the term “applicable taxable year” means any taxable year of the taxpayer beginning after December 31, 2017 , and before January 1, 2028 .